S46 



ANNUAL REGISTER, 1794-. 



blue, and the otlier yellow, witli 

 the difference, however, that the 

 colours ofthe shadows were reversed, 

 that which, with the yellow glciss, 

 was before yellow being now bine, 

 and that which was blue being- 

 yellow. 



I afterwards tried a glass of a 

 bright amethyst colour, and wassr.r- 

 prized to find that the shadows still 

 continued to be coloured blue and 

 yellow The yellow, it is true, 

 had a dirty purple cast? but the 

 blue, though a little inclining to 

 green, was nevertheless a clean, 

 bright, decided colour. 



Having no other coloured glass at 

 hand to push these particular inqui- 

 ries farther, I now removed tlie 

 candles, and opened two holes in 

 the upper parts of the window- 

 shutters of two neighbouring win- 

 dows, I let into the room from 

 above two beams of light fi'om diffe- 

 rent parts of the heavens, andplacing 

 the instrument in such a manner that 

 two distinct shadows were projected 

 by the cylinder upon the paper, I 

 was entertained by a succession of 

 very amusing appearances. The 

 shadows were tinged with an infi- 

 nite variety of themost unexpected, 

 and often most beautiful colours, 

 which continually varying, some- 

 times slowly, and sonieiimes with 

 inconceivable rapidity, absolutely 

 fascinated the eyes, and command- 

 ing the most eager attention, afford- 

 ed an enjoyment as new as it was 

 bewitching. It was a windy d?.y, 

 with flying clouds, and it seemed as 

 if every cloud that passed brought 

 with it another complete succession 

 of varying iiues, and most liarwo- 

 nious tints. If any colours could be 

 said to prrdo min.ite it was purples ; 

 but all the vaieties of browns, and 

 almost all the other colours I ever 



remcnibercd to have seen, ajipearecl d 

 in their turns, and there v/rrc even 

 colours u bich seemed to me to be 

 perfectly new. 



Ilefleciiiig upon the great variety 

 of colours observed in these ia«t ex- 

 periments, many of which did not 

 appear to have the least relation to 

 the apparent colours of the light by 

 which they were produced, I began 

 to SUnpect (hat the colours of the 

 shadows might, in many cases, not- 

 v.-ifhi.tanding their appaient brilli- 

 ancy, be mcrcl)- an optical decep- 

 tion, owing to contrast, or to some 

 effect of the other neighbouring co- 

 lours upon the eye. To determine- 

 this fact by a direct experiment, I 

 proceeded in the following manner. 

 Having, by making use of a flat 

 ruler instead of the cylinder, con- 

 trived to render the shadows mu.h 

 broader, I shut out of the room 

 every ray of day-light, and prepared 

 to make the experiment with two 

 Argand's lamps, well trimmed, and 

 which were both made to burn with 

 the greatest possible brilliancy; and 

 having assured myself that the light 

 they emitted was precisely of the 

 same colour, by th-e shadows be- 

 ing perfectly colourless which were 

 projected upon the white paper, i 

 directed a tube about 12 inches 

 long, and near an inch in diameter, 

 lined with black paper, against the 

 centre of one of the broad shadows ; 

 and looking through this tube with 

 one eye, wliile the other was closed, 

 I kept my attention fixed upon the 

 shadow, while an assistant repeated- 

 ly interposed a sheet of yellow glass 

 before the lamp whose light corres- 

 ponded to the shadow I observed, 

 and as often removed it. The re- 

 sult of the experiment was very 

 striking, and fully conlirmed my sus- 

 picions with respect to tlis fallacy 



of 



